JP2012530042A - Process for the preparation of surface-reacted calcium carbonate using weak acids, the products obtained and their use - Google Patents

Abstract

The present application relates to a process for preparing a surface-reacted calcium carbonate in an aqueous environment. The process according to the present invention aims at avoiding the mandatory implementation of medium-strong to strong acids. Another aspect of the present invention is directed to an aqueous suspension of surface-reacted calcium carbonate which is obtainable by the inventive process.

Description

  The present invention relates to the technical field of surface-reacted calcium carbonate products based on ground natural calcium carbonate (GNCC).

  In practice, calcium carbonate is used for various purposes such as paper coatings, fillers, extenders and pigments, as well as aqueous lacquers and paints, and water treatment, especially inorganic materials such as heavy metals and / or polycyclic compounds. As a means of removing pharmaceutical waste such as cholesterol and / or endocrine disrupting compounds (EDC), it is used in large quantities in the paper, paint, rubber and plastics industries.

  Over the past decade, a new class of calcium carbonate derivatives called “surface-reacted calcium carbonate” has been developed, providing a number of beneficial properties in application.

  “Surface-reacted calcium carbonate” is a material that includes calcium carbonate and an insoluble, at least partially crystalline, non-calcium carbonate salt extending from at least a portion of the surface of the calcium carbonate. The calcium ions that form the at least partially crystalline non-calcium carbonate salt are primarily derived from the calcium carbonate starting material that also functions to form the core of the surface-reacted calcium carbonate.

  In the art, several approaches for preparing such surface-reacted calcium carbonate products have been proposed.

US 6,666,953 B1 relates to pigments, fillers or minerals containing natural calcium carbonate treated by one or more suppliers of H ₃ O ⁺ ions and gaseous CO ₂ having a pK _a less than 2.5, When used as a pigment or coating filler for the paper, it allows a reduction in the weight of paper with a constant surface area without losing physical properties.

A variant of WO 2005/121257 A2 includes a plurality of compounds with at least one compound of the formula R—X, with calcium carbonate and medium to strong acids and with gaseous CO ₂ formed in situ and / or by external supply. Disclosed is a method for producing a dry mineral pigment, characterized in that it contains a product formed in situ by reaction.

Similarly, WO 2004/083316 A1 is a reaction product of calcium carbonate and said carbonate and one or more medium to strong H ₃ O ⁺ ion donors used in papermaking applications such as mass filling and / or paper coating. things and the well twice and / or more times of the product formed in situ by reaction between the carbonate and the reaction product of gaseous CO ₂ that which has been and / or externally supplied formed in situ as well as at least One aluminum silicate and / or at least one synthetic silica and / or at least one calcium silicate and / or sodium silicate and / or potassium silicate and / or lithium silicate, preferably one such as sodium silicate At least one silicate of a valent salt and / or at least Also refer to mineral pigments containing one aluminum hydroxide and / or at least one sodium and / or potassium aluminate.

  The above technique provides a means of structuring the surface of the GNCC starting material and significantly increasing the specific surface area by controlled deposition of at least partially crystalline calcium salt and a source of calcium for the deposition material It is of particular interest to those skilled in the art that is a GNCC mineral itself.

However, each involves the use of medium to strong acids characterized by a pK _a of less than 2.5 when measured at 20 ° C. Many of the acids presented as useful medium to strong acids are mineral acids, and preferred acids include phosphoric acid in particular.

  First, those skilled in the art will use alternative adjuncts given the availability and price of a given adduct subject to change over time, including unexpected changes that one skilled in the art must plan. There is always interest in new ways of preparing surface-reacted calcium carbonate materials.

  Secondly, with respect to occupational exposure limits established in cooperation with the International Chemical Safety Program and the European Commission, in particular the International Chemical Safety Card (ICSC) for phosphate issued by the International Center for Occupational Safety and Health (CIS) ), This acid is associated with a very low limit value (TLV) which corresponds to a time weighted average (TWA) of less than 1 ppm. This means that when this acid is used, especially on an industrial scale, specific and often troublesome precautions should be taken. Furthermore, those skilled in the art are aware of the dangers that regulations applied to such low TLV materials become more stringent over time and their use becomes impractical.

US Pat. No. 6,666,953 International Publication No. 2005/121257 International Publication No. 2004/083316 US Pat. No. 5,584,923 US Pat. No. 5,647,902 US Pat. No. 5,711,799 International Publication No. 97/08247 International Publication No. 98/20079 US Pat. No. 5,043,017 International Publication No. 99/02608 Unpublished European Patent Application No. 07213077.5

Harris, D.C. C. "Quantitative Chemical Analysis: 3rd edition", 1991, W.C. H. Freeman & Co. (USA), ISBN0-7167-2170-8 Transport in Porous Media (2006) 63: 239-259

  In the face of the above, the Applicant has surprisingly the possibility of developing a specific surface area comparable to the surface-reacted calcium carbonate prepared according to US 6,666,953 B1, but with moderate to strong acids such as phosphoric acid. We have found a method for preparing surface-reacted calcium carbonate that avoids the essential use of.

  The method of the present invention relies on a particular unexpected selection of adducts that are input according to a particular sequence of steps.

That is, the present method for preparing surface-reacted calcium carbonate in an aqueous environment comprises the following steps:
a) supplying at least one ground natural calcium carbonate (GNCC);
b) providing at least one water-soluble acid;
c) supplying gaseous CO ₂ ;
d) contacting the GNCC of step a) with the acid of step b) and the CO ₂ of step c);
(I) said acid of step b) is, when measured at 20 ° C., it has a respective 2.5 than 7 below pK _a, ionization of the first available hydrogen, and the available first With a corresponding anion that is capable of forming a water-soluble calcium salt, formed upon loss of hydrogen;
(Ii) After contact of the acid with the GNCC, in the case of a hydrogen-containing salt, the salt anion has _a pKa greater than 7 when measured at 20 ° C., with ionization of the first hydrogen available. It is characterized in that at least one water-soluble salt that can form a water-insoluble calcium salt is additionally provided.

  When the prior art refers to the contact of calcium carbonate with a weak acid, it takes a completely different goal and follows a fundamentally different method from the method of the present invention.

  In particular, US 5,584,923, US 5,647,902, US 5,711,799, WO 97 / 08247A1 and WO 98 / 20079A1, each enable use as a filler material in the production of neutral to weakly acidic paper. An acid-resistant calcium carbonate and a process for producing such acid-resistant calcium carbonate are described. Applicants point out that acid resistance is exactly the opposite of the goal of the present invention, where the method acts on GNCC, liberates calcium ions from GNCC, and then functions in the development of the surface area. To do.

  US 5,043,017 also relates to calcium carbonate that is acid stabilized by the addition of one calcium chelator and a conjugate base such as sodium hexametaphosphate, followed by the addition of an acid that may be a weak acid. This document, as mentioned above, is based not only on the goal of forming acid-resistant calcium carbonate, but also on the importance of supplying a calcium chelator or conjugate base to the calcium carbonate before the weak acid.

  WO 99 / 02608A1 describes a process for producing a high solids slurry of acid resistant precipitated calcium carbonate, where the solid slurry is treated with a chemical additive such as sodium aluminate to impart acid resistance to the calcium carbonate.

  For completeness, the Applicant describes an unpublished European patent application with application number 07213077.5 relating to a process for the preparation of surface-reacted calcium carbonate based on PCC.

Thus, the conventional technique is to prepare a high surface area surface-reacted calcium carbonate materials based on GNCC, at the same time, such as phosphoric acid, using a medium-strong to strong acids having a pK _a of less than measured at 20 ° C. 2.5 Seems to be silent on the economic way to avoid.

  The present invention aims to provide a method for preparing surface-reacted calcium carbonate as described in the application and defined in the claims.

Accordingly, one object of the present application is a method for preparing surface-reacted calcium carbonate in an aqueous environment comprising the following steps:
a) supplying at least one ground natural calcium carbonate (GNCC);
b) providing at least one water-soluble acid;
c) supplying gaseous CO ₂ ;
d) contacting the GNCC of step a) with the acid of step b) and the CO ₂ of step c);
(I) said acid of step b) is, when measured at 20 ° C., it has a respective 2.5 than 7 below pK _a, ionization of the first available hydrogen, and the available first With a corresponding anion that is capable of forming a water-soluble calcium salt, formed upon loss of hydrogen;
(Ii) After contact of the acid with the GNCC, in the case of a hydrogen-containing salt, the salt anion has _a pKa greater than 7 when measured at 20 ° C., with ionization of the first hydrogen available. The method is characterized in that at least one water-soluble salt that can form a water-insoluble calcium salt is additionally provided.

  “Milled natural calcium carbonate” (GNCC) in the sense of the present invention is obtained from a natural source, marble, chalk or limestone and is ground, screened and / or wet and / or dry subdivided with or without grinding aids. Calcium carbonate processed through treatment such as cyclization, for example, treatment with a cyclone.

  For purposes of this application, “water-insoluble” material is mixed with deionized water and filtered through a filter having a pore size of 0.2 μm at 20 ° C., and when the filtrate is recovered, 100 g of the filtrate is recovered from 95 to 100 Defined as a substance that provides no more than 0.1 g of recovered solid material after evaporation at 0C. A “water-soluble” material is defined as a material that results in recovery of more than 0.1 g of recovered solid material after evaporation of 100 g of the filtrate at 95-100 ° C.

“Acid” in the sense of the present invention is defined as Bronsted Lowry acid, ie a H ₃ O ⁺ ion supplier. An “acid salt” is defined as a hydrogen-containing salt that is partially neutralized by electron-positive elements other than hydrogen. A “salt” is defined as an electrically neutral ionic compound formed by anions and cations.

For the purposes of this application, pK _a is the symbol representing the acid dissociation constant associated with hydrogen that may be predetermined ionization in a given acid, the equilibrium in water at a given temperature of dissociation of this hydrogen from this acid Indicates the degree of nature. Such pK _a values are determined by Harris, D. et al. C. "Quantitative Chemical Analysis: 3rd edition", 1991, W.C. H. Freeman & Co. (USA), ISBN0-7167-2170-8, and other reference textbooks.

  According to the present invention, “surface-reacted calcium carbonate” is a substance comprising calcium carbonate and an insoluble and at least partially crystalline calcium salt of one or more anions of the water-soluble salt of (ii) above. is there. In preferred embodiments, the insoluble calcium salt extends from the surface of at least a portion of the calcium carbonate. The calcium ions that form the at least partially crystalline calcium salt of the anion are primarily derived from the calcium carbonate starting material. Such salts may include OH-anions and / or crystal water.

Preferred embodiments for step a) In step a) of the process according to the invention, at least one ground natural calcium carbonate (GNCC) is provided.

  Preferably, the GNCC is selected from the group consisting of marble, chalk, calcite, dolomite, limestone and mixtures thereof.

  In a preferred embodiment, said GNCC of step a) has a weight median of 0.01 to 10 μm, more preferably 0.5 to 2 μm, as measured according to the measurement method provided in the Examples section herein below. Has a diameter.

  In another preferred embodiment, GNCC is provided in the form of an aqueous GNCC suspension.

  In this preferred embodiment, the suspension has a pH of less than 11, more preferably less than 10.5, as measured according to the measurement method provided in the Examples section below.

  Preferably, the aqueous calcium carbonate suspension has a solids content of 10 wt% or more, more preferably 10 wt% to 80 wt%, based on the weight of the suspension. Applicants state as a finding that for very high solids it is a requirement to have enough water for the reaction to occur during and after step d). More preferably, the aqueous calcium carbonate suspension has a solids content in the range of 16 wt% to 60 wt%, more preferably in the range of 16 wt% to 40 wt%, based on the weight of the suspension.

  The suspension can be further stabilized by the addition of a dispersant. Conventional dispersants known to those skilled in the art can be used. The dispersant can be anionic, cationic or nonionic. A preferred dispersant is polyacrylic acid.

Preferred embodiments for step b) Step b) of the process of the invention refers to supplying at least one water-soluble acid. The acid, when measured at 20 ° C., respectively, has a 2.5 than 7 below pK _a, associated with the ionisation of the first available hydrogen, to form a water soluble calcium salt the It has the corresponding anion formed by the first available hydrogen deletion.

In a preferred embodiment, the water-soluble acid has a pK _a of from 5 to 2.6.

  In a more preferred embodiment, the water soluble acid is selected from the group consisting of acetic acid, formic acid, propanoic acid and mixtures thereof. In an even more preferred embodiment, the water soluble acid is selected from the group consisting of acetic acid, formic acid and mixtures thereof. In the most preferred embodiment, the water-soluble acid is acetic acid.

Said water-soluble acid of step b) is preferably the total amount corresponding to at least 1.5 × 10 ⁻⁴ mol of hydrogen atoms in the acid / m ² GNCC supplied in step a), more preferably step a). 2 × ^{10 -4} from 12 × ¹⁰ -4 mol of hydrogen atoms in the feed acid ^/ m 2 GNCC in, and most preferably, step a) 3 × ^{10 -4} at the feed acid ^/ m 2 GNCC in To a total amount corresponding to 10 × 10 ⁻⁴ mol of hydrogen atoms.

When the water-soluble salts in contact with said GNCC comprises one or more hydrogen atoms, a water-soluble salt of step b), the actual pK _a Toka no different associated hydrogen atoms salt, a complete dissociation of hydrogen ions Considering the mole equivalent of the hydrogen atom of the calculated salt, it can be introduced in a smaller amount. In such a case, the water-soluble acid is at least 1.5 × 10 ^{− in} acid / m ² GNCC in which the total molar equivalents of hydrogen atoms are supplied in step a) based on the water-soluble acid and hydrogen-containing salt. 2 × 10 ⁻⁴ to 12 × 10 ⁻⁴ mol hydrogen atoms in the acid / m ² GNCC charged in an amount corresponding to ⁴ mol hydrogen atoms, more preferably fed in step a), most preferably Is charged in a total amount corresponding to 3 × 10 ⁻⁴ to 10 × 10 ⁻⁴ mol of hydrogen atoms in the acid / m ² GNCC supplied in step a).

  Alternatively, the water-soluble acid of step b) is preferably the total amount corresponding to 5 to 40% by weight of pure acid, more preferably step a, based on the dry weight of GNCC supplied in step a) The total amount corresponding to 10 to 30% by weight equivalent of pure acid based on the dry weight of GNCC fed in), most preferably 15 to 25% based on the dry weight of GNCC fed in step a) Charged in a total amount corresponding to% equivalent of pure acid.

  Said water-soluble acid of step b) is preferably in the form of an aqueous solution having an acid concentration corresponding to 25 to 75%, more preferably 40 to 60%, determined as the equivalent of pure acid relative to the weight of the total solution. Supplied.

Preferred embodiment for step c) According to step c) of the process of the invention, gaseous CO ₂ is supplied.

  The required carbon dioxide can be formed in situ from the carbonate as a result of contacting the acid with GNCC. Alternatively or additionally, carbon dioxide can be supplied from an external source.

Preferably, the concentration of gaseous carbon dioxide in the aqueous suspension throughout the reaction is such that the ratio (suspension volume) :( volume of gaseous CO ₂ ) with respect to volume is from 1: 0.05 to 1:20. Preferably it is 1: 0.05 to 1: 5.

Preferred Embodiment for Step d) Step d) of the process of the invention refers to contacting the GNCC of step a) with the acid of step b) and the CO ₂ of step c).

  The acid is preferably added to the GNCC in one or more stages.

  If the GNCC is added to the acid, it is necessary to continue adding the GNCC fraction to the acid fraction, and this additional method until all the GNCC is in contact with all the acids. It is necessary to repeat.

  If an acid is used, the acid treatment and the treatment with carbon dioxide can be performed simultaneously and occur automatically. It is also possible to carry out the acid treatment according to the invention first, followed by treatment with carbon dioxide supplied from an external source.

  The addition of acid to GNCC can be carried out dropwise or in one step. In the case of dropwise addition, this addition is preferably carried out within 10 minutes. More preferably, the acid is added in one step.

Preferred embodiments for water-soluble acids After contacting the acid of step b) with the GNCC of step a) in step d), the hydrogen-containing salt has _a pK _a greater than 7 when measured at 20 ° C. In addition, at least one water-soluble salt is provided, with the ionization of the first hydrogen available, whose salt anion can form a water-insoluble calcium salt.

  The cation of the water-soluble salt is preferably selected from the group consisting of potassium, sodium, lithium and mixtures thereof. In a more preferred embodiment, the cation is sodium. Note that, depending on the charge of the anion, two or more of the cations can be present, resulting in an electrically neutral ionic compound.

  The anion of the water-soluble salt is preferably selected from the group consisting of phosphate, dihydrogen phosphate, monohydrogen phosphate, oxalate, silicate, mixtures thereof and hydrates thereof. In a more preferred embodiment, the anion is selected from the group consisting of phosphate, dihydrogen phosphate, monohydrogen phosphate, mixtures thereof and hydrates thereof. In a most preferred embodiment, the anion is selected from the group consisting of dihydrogen phosphate, monohydrogen phosphate, mixtures thereof and hydrates thereof.

The anions of the water-soluble salts are preferably charged in a total amount corresponding to at least 5 × 10 ⁻⁵ mol of anions / m ² GNCC supplied in step a). More preferably, the anion of the water-soluble salt is a total amount corresponding to 5 × 10 ⁻⁵ to 50 × 10 ⁻⁵ mol of anion / m ² GNCC supplied in step a), even more preferably, step a ) Is fed in a total amount corresponding to 10 × 10 ⁻⁵ to 30 × 10 ⁻⁵ mol of anion / m ² GNCC.

  The water-soluble salt can be added dropwise or in one step. In the case of dropwise addition, this addition is preferably carried out within 10 minutes. More preferably, the salt is added in one step.

Reaction environment Step d) and the addition of the water-soluble salt are preferably carried out in a stirred reactor under stirring conditions so as to generate a substantially laminar flow. Step d) and the addition of the water-soluble salt are preferably carried out in an aqueous environment having a temperature above 50 ° C, preferably above 60 ° C.

Product obtained by the method After the addition of said at least one water-soluble salt, the pH of the aqueous suspension measured at 20 ° C. is usually above 6.0, preferably above 6.5, more preferably 7 It may reach a value above 0.0, even more preferably above 7.5. In other words, the surface-reacted calcium carbonate is obtained as an aqueous suspension having a pH greater than 6.0, preferably greater than 6.5, more preferably greater than 7.0, and even more preferably greater than 7.5. . If the aqueous suspension is able to reach equilibrium, the pH is usually above 7. A pH above 6.0 can be adjusted without the addition of a base if stirring of the aqueous suspension is continued for a sufficient time, preferably 1 hour to 10 hours, more preferably 1 to 5 hours.

  Alternatively, the pH of the aqueous suspension can be increased to a value greater than 6 by addition of a base after carbon dioxide treatment before reaching an equilibrium state that occurs at a pH greater than 7. Any conventional base such as sodium hydroxide or potassium hydroxide can be used.

  The resulting surface-reacted calcium carbonate suspension can optionally be concentrated to a point where a dry surface-reacted calcium carbonate product is obtained. When the aqueous suspension described above is dehydrated, the resulting solid (ie, containing enough water so that it is not in fluid form, or even no water), the surface-reacted calcium carbonate is a cake Can be in the form of granules or powder. This solid product can be additionally treated with fatty acids or other hydrophobizing / lipophilicizing agents. This solid product can be washed with water.

  Thus, the surface-reacted calcium carbonate is preferably an insoluble, preferentially at least, anion of the at least one water-soluble salt extending from the surface of at least a portion of the calcium carbonate provided in step a). A suspension of surface-reacted calcium carbonate containing a partially crystalline calcium salt is obtained.

In a preferred embodiment, the surface-reacted calcium carbonate obtained by the method of the present invention is measured according to the measurement method provided in the Examples section below and is greater than 20 m ² / g, for example from 20 m ² / g to 200 m ^2. / G, more preferably more than 30 m ² / g, for example 30 m ² / g to 150 m ² / g, even more preferably more than 80 m ² / g.

In a preferred embodiment, the surface-reacted calcium carbonate has a BET specific surface area in the range of 20 to 150 m ² / g or 30 to 200 m ² / g and a median particle diameter in the range of 0.1 to 50 μm.

  Furthermore, the surface-reacted calcium carbonate is 0.1 to 50 μm, preferably 1 to 25 μm, more preferably 3 to 15 μm, even more preferably, as measured according to the measurement method provided in the Examples section below. Has a median particle diameter of 5 to 12 μm.

  Preferably, the surface-reacted natural calcium carbonate has an intraparticle porosity in the range of 20% to 40% by volume as measured by mercury porosimetry. Intraparticle porosity by mercury porosimetry is determined according to the following protocol: The tablet is suspended so that water is released by filtration through a fine filter membrane of 0.025 μm, resulting in a compressed tablet of pigment. Is produced from a suspension of surface-reacted natural calcium carbonate by applying a constant pressure to the surface for several hours. The tablets are removed from the apparatus and dried in an oven at 80 ° C. for 24 hours. Upon drying, a single portion of each tablet block is characterized by mercury porosimetry for porosity and pore size distribution using a Micromeritics Autopore IV mercury porosimeter. The maximum applied pressure of mercury is 414 Mpa, equal to a Laplace throat diameter of 0.004 μm (ie about nm). Mercury intrusion readings are corrected by mercury compression, penetration meter extension and sample solid phase compressibility. It is necessary to distinguish intraparticle pores from interparticle pores. For this purpose, it is necessary to confirm that the tablet structure is divided separately in the pore size distribution, i.e., that the diameters do not substantially overlap so that the interparticle and intraparticle pore sizes are distinguishable. Further details about the measurement method are described in Transport in Porous Media (2006) 63: 239-259.

  The surface-reacted calcium carbonate or slurry of the surface-reacted calcium carbonate of the present invention can be used in paper, tissue paper, plastic, paint, or as a controlled release or water treatment agent.

  The surface-reacted calcium carbonate obtained by the method of the present invention is preferably water to be purified, such as industrial waste water, drinking water, municipal waste water, brewery waste water or water in the paper industry, and any known to those skilled in the art. Contact is made by a conventional method.

  The surface-reacted calcium carbonate can be added as an aqueous suspension, such as the suspension described above. Alternatively, it can be added to the water to be purified in any suitable solid form, for example in the form of granules or powder or in the form of a cake.

  Water can contain organic impurities resulting from human soil, organic matter, soil, surfactants, as well as heavy impurities such as inorganic impurities, particularly iron-containing or manganese-containing compounds. Harmful components that can be removed from water by the purification method of the present invention include microorganisms such as bacteria, fungi, archaea, or protists.

  The following examples are intended to illustrate the invention without limiting its scope.

(Example)
Measurement Methods The following measurement methods are used to evaluate the parameters presented in the examples and claims.

Specific surface area of materials (SSA)
The specific surface area is measured via the BET method according to ISO 9277, using nitrogen, followed by conditioning the sample by heating at 250 ° C. for 30 minutes. Prior to such measurement, the sample is filtered, rinsed and dried in an oven at 90-100 ° C. for at least 12 hours before being crushed with a mortar and then massed at 130 ° C. until constant weight is observed. Install in balance.

Particle size distribution of non-surface-reacted calcium carbonate particulate material (ie GNCC) (mass% of particles of diameter <X) and weight median particle diameter (d ₅₀ )
The weight median particle diameter and particle diameter mass distribution of particulate matter such as GNCC is determined via sedimentation methods, ie, analysis of sedimentation behavior in a gravitational field. The measurement is performed with Sedigraph ™ 5120.

Methods and apparatus are known to those skilled in the art and are routinely used to determine the particle size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1% by weight Na ₄ P ₂ O ₇ . Samples were dispersed using a high speed stirrer and ultrasound.

Surface-reacted calcium carbonate median particle diameter (d ₅₀ )
The median particle diameter of the surface-reacted calcium carbonate is determined using a Malvern Mastersizer 2000 Laser Diffraction System.

PH of aqueous slurry
The pH of the aqueous suspension is measured using a standard pH meter at approximately 25 ° C.
Solid content of the aqueous slurry The solid content of the slurry (also known as “dry weight”) is a Moisture Analyzer HR73 marketed by Mettler-Toledo, with the following settings: temperature 120 ° C., automatic stop 3, Standard dry, determined by 5-20 g slurry.

  The following examples illustrate the prior art and involve contacting GNCC with phosphoric acid.

The calcium carbonate suspension is water and non-dispersed chalk (with a d ₅₀ of 1 μm, where 90% of the particles have a diameter of 2 μm or less (Sedigraph)) and the resulting aqueous suspension is suspended. Prepare by adding to a 20 L stainless steel reactor to have a solids content of 16% by dry weight relative to the total weight of the suspension. Thereafter, the temperature of the suspension is brought to 70 ° C. and maintained at 70 ° C.

Phosphoric acid in the form of a 10% solution is added to 10% by weight of dry calcium carbonate weight and approximately 3 × 10 ⁻⁴ mol equivalents of hydrogen / m ² with stirring at approximately 1000 rpm so that a substantially laminar flow is established. Add to calcium carbonate suspension over 10 minutes by peristaltic pump in an amount equivalent to GNCC. Following this addition, CO ₂ gas bubbles were observed to form in the suspension and rise through the suspension.

  The suspension is stirred for a further 5 minutes.

The resulting suspension is left overnight. The product has SSA = 24.0 m ² / g and d ₅₀ = 3.5 μm (Malvern).

  The following examples illustrate the prior art and involve contacting GNCC with phosphoric acid.

The calcium carbonate suspension is water and non-dispersed chalk (with a d ₅₀ of 3 μm, where 33% of the particles have a diameter of 2 μm or less (Sedigraph)) and the resulting aqueous suspension is suspended. Prepare by adding to a 100 L stainless steel reactor to have a solids content of 16% by dry weight relative to the total weight of the suspension. Thereafter, the temperature of the suspension is brought to 70 ° C. and maintained at 70 ° C.

While stirring at approximately 1000 rpm to establish a substantially laminar flow, the phosphoric acid in the form of a 30% solution is converted to 25% by weight of dry calcium carbonate weight and approximately 2.6 × 10 ⁻⁴ mol equivalents of hydrogen / m. ² Add to calcium carbonate suspension by peristaltic pump in an amount corresponding to GNCC over 10 minutes. Following this addition, CO ₂ gas bubbles were observed to form in the suspension and rise through the suspension.

  The suspension is stirred for a further 5 minutes.

The resulting suspension is left overnight. The product has SSA = 34.5 m ² / g and d ₅₀ = 7.9 μm (Malvern).

  The following examples illustrate the prior art and involve contacting GNCC with phosphoric acid.

The calcium carbonate suspension contains water and dispersed marble (having a d ₅₀ of 0.7 μm, where 90% of the particles have a diameter of 2 μm or less (Sedigraph)), and the resulting aqueous suspension is Prepare by adding to a 20 L stainless steel reactor to have a solids content of 16% by dry weight relative to the total weight of the suspension. Thereafter, the temperature of the suspension is brought to 70 ° C. and maintained at 70 ° C.

While stirring at approximately 1000 rpm so as to establish a substantially laminar flow, the phosphoric acid in the form of a 10% solution is 30% by weight of dry calcium carbonate weight and approximately 9 × 10 ⁻⁴ mol equivalents of hydrogen / m ² GNCC. Is added to the calcium carbonate suspension by a peristaltic pump over a period of 10 minutes. Following this addition, CO ₂ gas bubbles were observed to form in the suspension and rise through the suspension.

  The suspension is stirred for a further 5 minutes.

The resulting suspension is left overnight. The product has SSA = 35.0 m ² / g and d ₅₀ = 3.9 μm (Malvern).

  The following examples illustrate the invention.

The calcium carbonate suspension is water and non-dispersed chalk (with a d ₅₀ of 3 μm, where 33% of the particles have a diameter of 2 μm or less (Sedigraph)) and the resulting aqueous suspension is suspended. Prepare by adding to a 20 L stainless steel reactor to have a solids content of 16% by dry weight relative to the total weight of the suspension. Thereafter, the temperature of the suspension is brought to 70 ° C. and maintained at 70 ° C.

Acetic acid in the form of a 50% solution is mixed with 18.4% by weight of dry calcium carbonate and 3 × 10 ⁻⁴ mol equivalents of hydrogen / m ² GNCC with stirring at approximately 1000 rpm so that a substantially laminar flow is established. Is added to the calcium carbonate suspension through a separatory funnel over 1 minute. Following this addition, CO ₂ gas bubbles were observed to form in the suspension and rise through the suspension.

Thereafter, NaH ₂ PO ₄ . 2H ₂ O is converted into a calcium carbonate suspension over a period of 10 minutes by a peristaltic pump in an amount corresponding to 47.8% by weight of dry calcium carbonate weight and 3 × 10 ⁻⁴ mol of H ₂ PO ₄ anion / m ² GNCC. Add. Following this addition, the suspension is stirred for an additional 5 minutes.

The resulting suspension is left overnight. The product has SSA = 72.4 m ² / g and d ₅₀ = 7.1 μm (Malvern).

  The following examples illustrate the invention.

The calcium carbonate suspension is water and dispersed marble (having a d ₅₀ of 0.7 μm, where 90% of the particles have a diameter of 2 μm or less) and the resulting aqueous suspension is a suspension By adding to a 20 L stainless steel reactor to have a solids content of 16% by dry weight relative to the total weight of. Thereafter, the temperature of the suspension is brought to 70 ° C. and maintained at 70 ° C.

Acetic acid in the form of a 50% solution is mixed with 18.4% by weight of dry calcium carbonate and 3 × 10 ⁻⁴ mol equivalents of hydrogen / m ² GNCC with stirring at approximately 1000 rpm so that a substantially laminar flow is established. Is added to the calcium carbonate suspension through a separatory funnel over 1 minute. Following this addition, CO ₂ gas bubbles were observed to form in the suspension and rise through the suspension.

Thereafter, NaH ₂ PO ₄ . 2H ₂ O is added to the calcium carbonate slurry over 10 minutes by a peristaltic pump in an amount corresponding to 47.8% by weight of dry calcium carbonate weight and 3 × 10 ⁻⁴ mol of H ₂ PO ₄ anion / m ² GNCC. Following this addition, the suspension is stirred for an additional 5 minutes.

The resulting suspension is left overnight. The product has SSA = 81.6 m ² / g and d ₅₀ = 6.8 μm (Malvern).

  The following examples illustrate the invention.

The calcium carbonate suspension is water and non-dispersed chalk (with a d ₅₀ of 3 μm, where 33% of the particles have a diameter of 2 μm or less (Sedigraph)) and the resulting aqueous suspension is suspended. Prepare by adding to a 20 L stainless steel reactor to have a solids content of 16% by dry weight relative to the total weight of the suspension. Thereafter, the temperature of the suspension is brought to 70 ° C. and maintained at 70 ° C.

Acetic acid in the form of a 50% solution is mixed with 36.8% by weight of dry calcium carbonate and 6 × 10 ⁻⁴ mol equivalents of hydrogen / m ² GNCC with stirring at approximately 1000 rpm so that a substantial laminar flow is established. Is added to the calcium carbonate suspension through a separatory funnel over 1 minute. Following this addition, CO ₂ gas bubbles were observed to form in the suspension and rise through the suspension.

Thereafter, Na ₂ HPO ₄ in the form of 30% solution / slurry is added by a peristaltic pump in an amount corresponding to 43.5% by weight of calcium carbonate weight and 3 × 10 ⁻⁴ mol of HPO ₄ anion / m ² GNCC for 10 minutes. Add to the calcium carbonate suspension. Following this addition, the suspension is stirred for an additional 5 minutes.

The resulting suspension is left overnight. The product has SSA = 69.6 m ² / g and d ₅₀ = 7.5 μm (Malvern).

  The following examples illustrate the invention.

The calcium carbonate suspension is water and non-dispersed chalk (with a d ₅₀ of 3 μm, where 33% of the particles have a diameter of 2 μm or less (Sedigraph)) and the resulting aqueous suspension is suspended. Prepare by adding to a 20 L stainless steel reactor to have a solids content of 16% by dry weight relative to the total weight of the suspension. Thereafter, the temperature of the suspension is brought to 70 ° C. and maintained at 70 ° C.

Acetic acid in the form of a 50% solution is mixed with 6.1% by weight of dry calcium carbonate weight and 1 × 10 ⁻⁴ mol equivalent of hydrogen / m ² GNCC with stirring at approximately 1000 rpm so that a substantially laminar flow is established. Is added to the calcium carbonate suspension through a separatory funnel over 1 minute. Following this addition, CO ₂ gas bubbles were observed to form in the suspension and rise through the suspension.

Thereafter, NaH ₂ PO ₄ . 2H ₂ O is added to the calcium carbonate slurry by a peristaltic pump over a period of 10 minutes in an amount corresponding to 15.9% by weight of calcium carbonate and 1 × 10 ⁻⁴ mol of H ₂ PO ₄ anion / m ² GNCC. Following this addition, the suspension is stirred for an additional 5 minutes.

The resulting suspension is left overnight. The product has SSA = 33.5 m ² / g and d ₅₀ = 6.0 μm (Malvern).

Claims (30)

A method for preparing surface-reacted calcium carbonate in an aqueous environment comprising the following steps:
a) supplying at least one ground natural calcium carbonate (GNCC);
b) providing at least one water-soluble acid;
c) supplying gaseous CO ₂ ;
d) contacting the GNCC of step a) with the acid of step b) and the CO ₂ of step c);
(I) said acid of step b) is, when measured at 20 ° C., it has a respective 2.5 than 7 below pK _a, ionization of the first available hydrogen, and the available first With a corresponding anion that is capable of forming a water-soluble calcium salt, formed upon loss of hydrogen;
(Ii) After contact of the acid with the GNCC, in the case of a hydrogen-containing salt, the salt anion has _a pKa greater than 7 when measured at 20 ° C., with ionization of the first hydrogen available. A method characterized in that at least one water-soluble salt that can form a water-insoluble calcium salt is additionally provided.   The method of claim 1, wherein the GNCC is selected from the group consisting of marble, chalk, calcite, dolomite, limestone, and mixtures thereof.   3. A method according to claim 1 or 2, characterized in that the GNCC of step a) has a weight median diameter of 0.01 to 10 [mu] m, more preferably 0.5 to 2 [mu] m.   4. A process according to any of claims 1 to 3, characterized in that the GNCC is supplied in the form of an aqueous GNCC suspension.   5. A method according to claim 4, characterized in that the suspension has a pH of less than 11, more preferably less than 10.5.   The suspension is at least 10% by weight, preferably from 10% to 80%, more preferably from 16% to 60%, even more preferably from 16% by weight, based on the weight of the suspension. 6. A process according to claim 4 or 5, characterized in that it has a solids content in the range of 40% by weight.   7. A method according to any of claims 4 to 6, characterized in that the suspension is stabilized by the addition of a dispersant. Wherein the water-soluble acid characterized by having a pK _a of from 5 to 2.6 A method according to any of claims 1 to 7 in step b).   The water-soluble acid is selected from the group consisting of acetic acid, formic acid, propanoic acid and mixtures thereof, more preferably selected from the group consisting of acetic acid, formic acid and mixtures thereof, most preferably acetic acid. 8. A method according to any of claims 1 to 7, characterized in that The water-soluble acid is preferably the total amount corresponding to at least 1.5 × 10 ⁻⁴ mol of hydrogen atoms in acid / m ² GNCC supplied in step a), more preferably the acid supplied in step a). / ^m 2 2 × ^{10 -4} from 12 × ¹⁰ -4 mol of hydrogen atoms in GNCC, most preferably, step a) 3 × ^{10 -4} from 10 × 10 with acid ^/ m 2 GNCC supplied in ^- 10. The method according to claim 1, wherein a total amount corresponding to ⁴ mol of hydrogen atoms is added.   Said water-soluble acid of step b) is fed in a total amount corresponding to 5 to 40% by weight equivalent of pure acid, more preferably in step a), based on the dry weight of GNCC fed in step a). A total amount corresponding to 10 to 30% by weight of pure acid based on the dry weight of GNCC, most preferably 15 to 25% by weight of pure acid based on the dry weight of GNCC supplied in step a) The method according to any one of claims 1 to 9, characterized in that it is introduced in a total amount corresponding to an acid.   Said water-soluble acid of step b) is supplied in the form of an aqueous solution having an acid concentration corresponding to 25 to 75%, more preferably 40 to 60%, determined as the equivalent of pure acid relative to the weight of the total solution. 12. A method according to any of claims 1 to 11, characterized in that   13. Process according to any of claims 1 to 12, characterized in that during step d) the acid of step b) is added to the GNCC in one or more steps, preferably in one step.   The method according to any one of claims 1 to 13, characterized in that the cation of the water-soluble salt is selected from the group consisting of potassium, sodium, lithium and mixtures thereof, more preferably sodium.   The anion of the water-soluble salt is a group consisting of phosphate, dihydrogen phosphate, monohydrogen phosphate, oxalate, silicate, mixtures thereof and hydrates thereof, more preferably phosphate, Selected from the group consisting of dihydrogen phosphate, monohydrogen phosphate, mixtures thereof and hydrates thereof, most preferably selected from the group consisting of dihydrogen phosphate, monohydrogen phosphate, mixtures thereof and hydrates thereof 15. A method according to any of claims 1 to 14, characterized in that Wherein the anion of the water-soluble salts, the total amount corresponding to at least 5 × ¹⁰ -5 mol of anion ^/ m 2 GNCC supplied in step a), preferably anion ^/ m 2 GNCC supplied in step a) 5 Charged in a total amount corresponding to × 10 ⁻⁵ to 50 × 10 ⁻⁵ mol, more preferably a total amount corresponding to 10 × 10 ⁻⁵ to 30 × 10 ⁻⁵ mol of anion / m ² GNCC supplied in step a) 16. A method according to any of claims 1 to 15, characterized in that   The method according to any one of claims 1 to 16, characterized in that the water-soluble salt is added in one step.   18. Step d) and the addition of the water-soluble salt are preferably carried out in a stirred reactor under stirring conditions so as to generate a substantially laminar flow. the method of.   19. The method according to any of the preceding claims, characterized in that step d) and the addition of the water-soluble salt are preferably carried out in an aqueous environment having a temperature above 50 ° C, preferably above 60 ° C. the method of.   20. A process according to any one of the preceding claims, characterized in that the aqueous suspension is concentrated after step d).   An aqueous suspension of surface-reacted calcium carbonate obtained by the method according to any one of claims 1 to 20.   Characterized in that the pH of the aqueous suspension is greater than 6.0, preferably greater than 6.5, more preferably greater than 7.0, even more preferably greater than 7.5 when measured at 20 ° C. The aqueous suspension of claim 21. 23. The surface-reacted calcium carbonate has a specific surface area of greater than 20 m < ² > / g, preferably greater than 30 m < ² > / g, more preferably greater than 80 m < ² > / g. Aqueous suspension. The surface-reacted calcium carbonate is in the range of from ^{20 m} 2 / g of 200 meters ² / g, preferably characterized in that it has a specific surface area in the range of from ^{30 m} 2 / g of 150 meters ² / g, according to claim 21 or 22 An aqueous suspension as described in 1. The surface-reacted calcium carbonate, and having a median particle diameter in the range from 150 meters ² / g or 30 to 20 from the specific surface area and 0.1 in a range of 200 meters ² / g of 50 [mu] m, according to claim 21 Or an aqueous suspension according to 22.   25. The surface-reacted calcium carbonate has a median particle diameter of 0.1 to 50 μm, preferably 1 to 25 μm, more preferably 3 to 15 μm, even more preferably 5 to 12 μm. An aqueous suspension according to any of the above.   27. The surface-reacted calcium carbonate has an intraparticle porosity in the range of 20% to 40% by volume as measured by mercury porosity measurement. Aqueous suspension.   Solid surface-reacted calcium carbonate obtained by drying the aqueous suspension according to any one of claims 21 to 27.   A treated surface-reacted calcium carbonate obtained by treating the solid surface-reacted calcium carbonate of claim 28 with a fatty acid or other hydrophobizing / lipophilic agent.   28. An aqueous suspension of surface-reacted calcium carbonate according to any of claims 21 to 27, in paper, tissue paper, plastic, paint, or as a controlled release or water treatment agent, solid surface reaction according to claim 28. Use of calcium carbonate or the treated surface-reacted calcium carbonate of claim 29.